CONCHIFERA. 



253 



and other foreign bodies, lining sometimes their dwelling 

 with a shelly substance. — Marine. 



Pholas. Lin. — Shell gaping at both ends, particularly 

 anteriorly, equivalve and transverse, having a 

 flat, recurved, spoon-shaped process in each 

 valve below the bosses, which are near one 

 end of the valves, covered by a callosity, and 

 having also accessory pieces attached ; pallial 

 impression deeply sinuated. Animal having 

 the lobes of the mantle united in front except 

 for a small space for the foot, reflected dor- 

 sally to cover the bosses ; a long siphon divided 

 near the extremity, and bordered with cirrhi ; 

 foot short, thick, and truncated at the end. — 

 42 species * ; also fossil. P7wlas dactylus - 



These molluscs inhabit indurated mud or clay, wood, 

 and stone, into which they bore when young, and in 

 which they continue to reside until their death. It was not 

 decidedly known in what manner these soft-bodied ani- 

 mals, inhabiting so fragile a tenement, were able to pene- 

 trate hard substances, whether by the aid of a corrosive 

 agent, or by the action of the valves, which in most cases 

 are rough and able to rasp away particles of rock, when 

 rubbed against it. Mr. Forbes inclines to the latter 

 opinion : he says there is no evidence of a secreted 

 solvent. Mr. Hancock, however, has discovered that all 

 the boring mollusks have the foot and front part of the 

 mantle armed with little crystalline bodies, which form 

 rubbing or rasping instruments of very great power, and 

 that it is by this means they form their habitation in the 

 solid rock.f They are, from their habits, exceedingly 



* Sowerby's Thesaurus. 



| See an interesting paper on this subject in the Annals of Nat, 

 Hist. 2nd vol. 2nd series. 



